In conventional hydraulic systems, the load is controlled by an actuator with one or more working chambers. The pressure of the hydraulic fluid in the system acts on the effective area of the working chamber and generates a force acting on the load via the actuator. The magnitude of the force will depend on both the effective area and the pressure level of the hydraulic fluid. Typical examples of applying the generated force are transferring, lifting and lowering a load. The load is, for example, a part of a structure, an apparatus or a system to be moved, or a piece to be moved by said part.
The control of the pressure level may be based on lossy control, and the control of the magnitude of the force generated by the actuator is performed by stepless control of the pressure level of the working chambers. Thus, the pressure level of the working chamber is adjusted by throttling the flow of hydraulic fluid entering or leaving the working chamber, by means of control valves.
Conventional hydraulic systems have a pressure side in which the pressure is controlled and which only produces a volume flow of hydraulic fluid, as well as a return side which only receives the volume flow and in which the prevailing pressure level is as low as possible, a so-called tank pressure, or a counter pressure needed for controlling the load. The pressure and return sides are equipped with control valves for controlling said pressure level, counter pressure and load.
Problems in conventional systems include losses in hydraulic output of the control valves, caused by throttling of the flow of hydraulic fluid, that is, the throttle control.
Hydraulic systems based on non-throttled control are also known, which utilize actuators with two or more working chambers, two or more pressure levels of hydraulic fluid, and control interfaces which are opened and closed. The control interfaces connect the desired pressure level to each working chamber of the actuator, and each working chamber generates a force component corresponding to said pressure level. The combined force components of the actuator make up the sum force of the actuator. There are many of these sum forces, they are discrete and constitute force steps which may be used to control the load connected to the actuator, and the state of the load, and this is referred to as so-called force control.
An example of such a hydraulic system based on non-throttled control is presented in WO 2010/040890 A1.
In hydraulic systems based on the non-throttled control, the pressure levels of the hydraulic fluid vary in several different working chambers simultaneously, which in some situations of coupling between the force steps may cause unnecessary variation or vibration in the sum force of the actuator.